Sagging concrete pool deck

I have a concrete pool deck adjacent to my house. The deck is roughly 40'x40' and adjoins the center of the rear of the house. It is also screen-enclosed. The lot has a slope, right-to-left facing the back of the lot, so that the pool deck is just over the grade on the right and a good 3' over the grade on the left.

When I first moved in, there were large, bushy spruce trees just outside the pool deck. They had overgrown and the bottoms of the trees pushed through the screens. The trees were about 15' tall. I removed the trees (I made that sound easy didn't I?), but what I didn't anticipate was that without the trees, the berm that had been built up around the deck (about 3 feet wide) became unstable and quickly eroded.

We live in central Florida, so the ground is sand. In under two years, the left back corner of the deck's berm had completely eroded away and the slab began to undermine. Now that corner of the deck has two hairline cracks from the edge of the deck to the pool, about ten feet from the corner on either side where the pool is closest to the edge.

I know that if I don't do something, it won't be long before the problem becomes quite serious. Like a lot of folks these days, I don't have a lot of money to use for home repairs, so I'm looking for an inexpensive, DIY solution.

One thing I considered is digging a trench beneath the slab at the corner, perhaps four feet in, then placing a 4x4 at the bottom of the trench a couple of feet below the slab bottom, then propping another 4x4 against the bottom of the slab, then putting a hydraulic jack between them and jacking the slab up just a hair to compensate for the settling. Then I would brace the front and back of the 4x4's with shorter pieces of 4x4 to bear the load. I could then remove the jack and fill the trench with concrete.

Is that a fool plan? Can you think of a better way that doesn't involve a contractor and major expense?

Needless to say, once this is done I plan to recreate the berm using landscaping timbers and concrete to prevent a reoccurence. Thanks for your thoughts in advance.

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You can use what's called "flowable fill"....Really soupy concrete. With the slab jacked up to where it is supposed to be (good luck), and forms to contain the concrete, the concrete will find its way under the slab and fill the undermined area. I'd also consider having some pea gravel on hand to fill in gaps.

Erect a solid retaining structure with good drainage to ensure that the earth doesn't continue to erode.